Port label switching

ABSTRACT

A communications switch comprising a plurality of numerically identified input traffic ports, a plurality of numerically identified output traffic ports, at least one significant label extractor and at least one numerical processor, the communications switch being arranged whereby each message entering the communication switch by a numerically identified input traffic port contains a header, which header contains a label stack, which label stack includes at least one valid label, of which one valid label is a significant label. The numerical value of the significant label contained within the header of a particular message which entered the communications switch via a particular numerically identified input traffic port is extracted by the at least one significant label extractor and is supplied to one of the at least one numerical processors. The numerical processor uses the significant label of the particular message and the numerical value of the particular numerically identified input traffic port to form a numerical result which directly equates to the number of the numerically identified output traffic port by which the particular message leaves the communications switch and wherein the numerical result is equal to the modulo addition of the numerical value of the significant label and the numerical value of the particular numerically identified input traffic port.

It is often desirable for Communication Networks to accommodate changesin the source and/or destination of traffic and the total quantity oftraffic. An example of this is a connection oriented TelecommunicationNetwork which establishes and clears calls which have been initiated bya mechanism that originally employed physical dialling, and will bereferred to in the present application as “Dial-Up”. Another example isa Data Network used to transfer data of widely varying amounts betweenmany computers which could operate using the Internet Protocol (IP). Itcan also be desirable to have redundancy mechanisms so that a level ofservice can still be achieved even when some failures have occurredwithin the Network.

Once a path has been established across a Dial-Up Network, it isexpected to remain established for at least several seconds and perhapsmany minutes or hours; and also to have a guarantee of a constant duplexdata rate, whereas an IP Network has to handle bursts of simplex data.Many traditional Dial-Up Networks impose delay propagation restraints inorder to ensure that good communications are not impaired, for exampleby echo.

Trying to use common equipment to carry in a reliable manner bothDial-Up traffic and IP traffic, without significantly impairing eitherof the two different types of traffic, creates so many problems that itis usually advisable not to mix them directly in the same multiplex,{for example Dial-Up and IP traffic both carried as IP} although ofcourse they can be carried separately by the same transmission Network{e.g. carried by separate Virtual Containers (VC) in a SynchronousDigital Hierarchy (SDH) Network}.

One of the reasons for not directly mixing Dial-Up traffic and IPtraffic, is that they require different algorithms within the Network:Dial-Up traffic requires call processing to establish calls; whereas IPtraffic requires the forwarding of individual packets.

It is essential to note the fundamental difference between carrying IPtraffic across a Network and carrying call based PSTN traffic across aNetwork, namely Dial-Up. A Dial-Up Network has to be able to ensurebandwidth is available for the duration of each call. An IP Network hasto be able to send a packet from any input to any output, so in effectfor IP traffic, paths are permanently enabled from all inputs to alloutputs, but there is no guarantee of bandwidth. A solution will bedescribed which enables IP and Dial-Up traffic to be carried across thesame Network, provided certain arrangements are used.

For Dial-Up traffic and IP traffic to share a common Network, if theentire algorithm processing (for call processing and forwarding) couldbe done before entry into the common Network then it would still bepossible to use different algorithms for the Dial-Up traffic and the IPtraffic. The type of network topology employed by the common Networkwill affect the difficulty in achieving this.

Some arrangements for regular topological networks have either alreadybeen Patented or are subject to Patent Applications. Patent No.GB2343582B describes Partially Interconnected STAR Networks and PatentApplication No. WO 01/84877 describes Partially Interconnected FLATNetworks. Patent Application No. GB0130729.7 describes Packet TrafficOptimisation. Patent Application No. GB0130730.5 combines several of theabove techniques and details regarding this Patent and these PatentApplications are included herein for reference. Patent Application No.GB0130730.5 describes a partially interconnected network comprising aplurality of nodes, which nodes include either;

-   -   (a) Allocated Nodes and Star Nodes (STARs), wherein the        Allocated Nodes are each allocated to one of a number of Areas        (AREAs) and the partially interconnected network also comprises        point to point interconnections between the Allocated Nodes and        the STARs, where the number of AREAs with Allocated Nodes        interconnected to an individual Star forms the number of Routes        (ROUTEs) from an individual STAR, the Allocated Nodes of a first        of the AREAs being interconnected to a set comprising some, but        not all, of the STAR Nodes, and wherein further of the AREAs are        similarly interconnected to further sets each comprising STAR        Nodes and where there is at least one interconnection choice        (CHOICE) between any two Allocated Nodes in different AREAs and        where an interconnection route comprises two point to point        interconnections interconnected in series by a STAR Node; or    -   (b) at least six Topological Nodes, wherein a Topological Node        is a single Physical Node or a group of interconnected Physical        Nodes or part of a Physical Node or a group of interconnected        Physical Nodes and parts of Physical Nodes, each Topological        Node having at least three point-to-point Topological Links        connecting it to some but not all of the plurality of        Topological Nodes and where there is at least one Choice of        routing between any two Topological Nodes and where a Choice of        routing comprises either two point-to-point Topological Links        connected in series at another of the Topological Nodes or a        direct point-to-point Topological Link between the two        Topological Nodes; wherein at least one of the plurality of        nodes includes a switching means arranged to carry out a Simple        Transit Core Function and three or more of the plurality of        nodes include a Single Link Interface which Single Link        Interface has associated Output Attributes and/or Input        Cognisant Attributes where each Simple Transit Core Function at        one node is not logically connected to another Simple Transit        Core Function at another node and each Simple Transit Core        Function at one node is logically connected to at least three        Single Link Interfaces at other nodes and wherein the nodes        including Single Link Interfaces which are connected to one        instance of a node arranged to carry out a Simple Transit Core        Function are controlled by respective Intercommunicating        Connection Acceptance Control Processes according to the        respective Output Attributes and/or Input Cognisant Attributes.

A network which does not require the algorithm processing to be done bythe network switches may be constructed from a network of similarmultiple port communication switches.

According to the present invention there is a communications switchcomprising, a plurality of numerically identified input traffic ports, aplurality of numerically identified output traffic ports, at least onesignificant label extraction means and at least one numerical processor,the communications switch being arranged whereby each message enteringthe communication switch by a numerically identified input traffic portcontains a header, which header contains a label stack, which labelstack includes at least one valid label, of which one valid label is asignificant label and wherein the numerical value of the significantlabel contained within the header of a particular message which enteredthe communications switch via a particular numerically identified inputtraffic port is extracted by one of the at least one significant labelextraction means and is supplied to one of the at least one numericalprocessors which numerical processor uses the significant label of theparticular message and the numerical value of the particular numericallyidentified input traffic port to form a numerical result which directlyequates to the number of the numerically identified output traffic portby which said particular message leaves the communications switch.

The present invention will now be described by way of example, withreference to the accompanying figures, in which:—

FIG. 1 shows a practical Partially Interconnected 11 STAR Network, withsplit AREA and Allocated Nodes according to a prior art invention;

FIG. 2 shows FIG. 1 with two Gateways attached to the same AllocatedNode;

FIG. 3 shows FIG. 1 with two Gateways attached to different AllocatedNodes in the same AREA;

FIG. 4 shows FIG. 1 with two Gateways attached to different AllocatedNodes in different AREAs;

FIG. 5 shows a combination of FIGS. 2, 3 and 4;

FIG. 6 shows a Partially Interconnected FLAT Network with 16 TopologicalNodes according to a prior art invention;

FIG. 7 shows the Partially Interconnected FLAT Network of FIG. 6 redrawnwith Point Meshes according to a prior art invention;

FIG. 8 shows FIG. 7 with three Gateways attached to four TopologicalNodes;

FIG. 9 shows a diagrammatic view illustrating an example of RelativePort Label Switching;

FIG. 10 shows a diagrammatic view illustrating the use of Service DomainPermits with Relative Port Label Switching;

FIG. 11 shows a diagrammatic view illustrating the summation of ServiceDomain Permits;

FIG. 12 shows a diagrammatic representation of Relative Port Labels at aGateway;

FIG. 13 shows a diagrammatic view illustrating the action of RelativePort Label Switching at an Originating Allocated Edge Node;

FIG. 14 shows a diagrammatic view illustrating the action of RelativePort Label Switching at an Originating AREA Node;

FIG. 15 shows a diagrammatic view illustrating the action of RelativePort Label Switching at an Originating STAR Node;

FIG. 16 shows a diagrammatic view illustrating the action of RelativePort Label Switching at an Terminating AREA Node;

FIG. 17 shows a diagrammatic view illustrating the action of RelativePort Label Switching at an Terminating Allocated Edge Node;

FIG. 18 shows a diagrammatic view illustrating the generation of aReverse Stack of Relative Port Labels at a Gateway.

Patent Application No. 0130730.5 described some Networks which employPartially Interconnected STAR Networks and Partially Interconnected FLATNetworks.

A given example of a STAR Network by the above Patent Application was:Allocated Node Split AREA STAR Split AREA Allocated Node MP CrossconnectSTC Crossconnect MP

A given example of a FLAT Network by the above Patent Application was:MP/STC Point Mesh MP/STC Point Mesh MP/STC MP Crossconnect STCCrossconnect MP

Where MP is a main processing node.

Where STC is a node containing a Simple Transit Core.

Both these types of Networks can involve traversing 5 nodes, of whichthe middle 3 nodes have been arranged to be two fixed crossconnects anda Simple Transit Core function.

FIG. 1, of the present Patent Application, shows an example of a STARNetwork. It was also FIG. 10 of Patent Application No. GB0130730.5. Thisis a small Network compared with some STAR Networks that can be formedfrom the BIBDs (Balanced Incomplete Block Designs) listed in THE CRCHANDBOOK OF COMBINATORIAL DESIGNS edited by Charles J. Colburne andJeffrey H. Dinitz.

FIG. 1 of the present Patent Application classifies the nodes into: EdgeNodes; AREA Nodes; and STAR Nodes. It is a twin CHOICE Network as thereare a CHOICE of 2 STARs that can be traversed when going from an EdgeNode in one AREA to an Edge Node in another AREA. For example to go froman Edge Node in AREA 9 to an Edge Node in AREA 4: STAR 9 or STAR 3 canbe traversed. There are also options for which AREA Nodes are used. Soin this example 5 Nodes in total are traversed.

FIG. 2 shows a simple connection between two Gateways on the same EdgeNode. In this case only the Edge Node is traversed.

FIG. 3 shows a connection between two Gateways on different Edge Nodeswhich are both connected to the same pair of AREA Nodes. In this casetwo Edge Nodes and one AREA Node are traversed; a total of 3 switches.

FIG. 4 shows a connection between two Gateways on different Edge Nodeswhich are connected to different pairs of AREA Nodes. In this case twoEdge Nodes, two AREA Nodes and one STAR Node are traversed; a total of 5switches.

In consequence in order to traverse a regular STAR topology Network, ofthe kind described, 1, 3 or 5 nodes have to be traversed to reachGateways A, B or C respectively as shown in FIG. 5.

FIG. 6 of the present Patent Application shows an example of a FLATNetwork. It was also FIG. 24 of Patent Application No. GB0130730.5. Thishas 16 Nodes to which Gateways may be attached. It can be considered asbeing formed from 8 Meshes each of 4 Nodes namely:

-   -   1, 2, 3 & 4 - - - 5, 6, 7 & 8 - - - 9, 10, 11 & 12 - - - 13, 14,        15 & 16    -   1, 5, 9 & 13 - - - 2, 6, 10 & 14 - - - 3, 7, 11 & 15 - - - 4, 8,        12 & 16

FIG. 7, of the present Patent Application, shows the above example of aFLAT Network, but with the Meshes shown as Point Meshes. It was alsoFIG. 25 of Patent Application No. GB0130730.5. This has 16 Nodes towhich Gateways may be attached and the 8 Point Mesh Nodes to whichGateways may not be attached.

This is a small Network compared with some FLAT Networks that can beformed from the SRGs (Strongly Regular Graphs) listed in THE CRCHANDBOOK OF COMBINATORIAL DESIGNS edited by Charles J. Colburne andJeffrey H. Dinitz.

Traversing this FLAT Network also requires 1, 3 or 5 nodes to betraversed to reach Gateways A, B or C respectively, as shown in FIG. 8.

To reach Gateway A traverse

-   -   Node 1;

To reach Gateway B traverse

-   -   Node 1, Node (1, 5, 9 & 13) and Node 5;

To reach Gateway C traverse

-   -   Node 1, Node (1, 2, 3 & 4), Node 4, Node (4, 8, 12 & 16) and        Node 8.

Returning to FIG. 4, assuming each Allocated Edge node has at least onegateway, then an Allocated Edge node must have at least 3 ports. Eachsplit AREA node is shown with 9 ports, and each STAR with 10 ports. Soto specify the route across the Network, as shown in FIG. 4, from onegateway to another gateway, requires in effect 5 address fields say of 4bits each.

So:

the first of the five fields defines the output port from the firstAllocated Edge Node; the second of the five fields defines the outputport from the first AREA Node; the third of the five fields defines theoutput port from the STAR Node; the fourth of the five fields definesthe output port from the second AREA Node; the fifth of the five fieldsdefines the output port from the final Edge Allocated Node.

Asynchronous Transfer Mode (ATM) is a multiplex method that was designedso that it could be operated by Dial-Up call control, although theformat uses fixed length packets called cells rather than fixed timedivision multiplexing. The addressing range of ATM has a maximum size of28 bits and is arranged as two fields one of 12 bits (or 8 bits for UserNetwork Interfaces) of Virtual Path Indicator (VPI) and the other of 16bits of Virtual Connection Indicator (VCI). Because ATM was designedwith call control in mind the addressing range only needed to besufficient to indicate individual connections within the multiplex usingthe VCI field: the VPI field could be used for traversing any ATMcross-connects to the next switch acting under call control. ATM was notdesigned with having say 5 separate address fields where each addressfield is to define the output port of 5 switches to be traversed.

ATM uses Header Translation Tables because a particular value in part ofthe address field does not always directly correspond to a particularoutput port. A key feature of the present Patent Application is that aspecific part of the address contained in the header directly definesthe output port to be used to exit from the switch.

Port Label Switching is the name that is being given to a technique inthe present Patent Application whereby the header of a cell, frame orpacket contains a stack of Labels, where each Label is intended tospecify directly the numerical identities of output traffic ports. Forexample where a Label contains the numerical value 167; this means thatthe cell, frame or packet should leave the switch that the label relatesto via the output traffic port with the numerical identity of 167. Inthe present Patent Application the label, that a switch should act upon,is call the Significant Label. The Significant Label is one of thelabels contained within a stack of labels. However although such atechnique can be used another technique is rather more useful.

Relative Port Label Switching is similar to Port Label Switching, butwith an important difference. The numerical identity of the outputtraffic port that should be used to leave the switch is not justdependent on the numerical value of the Significant Label, but it isalso dependent on the numerical identity of the input traffic port thatwas used to enter the switch. Basically the numerical value of theSignificant Label and the numerical identity of the input traffic portare added together, using Modulo Addition, to form the numericalidentity of the output traffic port.

Relative Port Label Switching requires a port label for every switchtraversed. For simplicity FIG. 9 shows only 3 labels in the header.

Although directly addressed port labels could be used Relative PortLabels will be described as they have a particular advantage.

For Relative Port Label Switching, the header of a packet must contain aStack of Relative Port Labels and a Service Domain Permit Number. FIG. 9shows the packet being sent from left to right with the first label (+1)being before the other labels in the Stack and after the Service DomainPermit Number.

When a packet arrives at an Input Port of a switch the numerical valueof the Significant Relative Port Label will be used. The numerical valueof the Significant Relative Port Label received is added to thenumerical identity of the input traffic port (Modulo Addition) todetermine the numerical identity of the output traffic port.

The switches shown in FIG. 9 are 4 port switches.

-   At the first switch in FIG. 9: 2+1=3 so the path traverses from Port    2 to Port 3.-   At the second switch in FIG. 9: 1+3=4 so the path traverses from    Port 1 to Port 4.-   At the third switch in FIG. 9: 1+0=1 so the path traverses from Port    1 to Port 1.

The addition performed has to be a modulo addition because in thisexample if the result of the addition is greater than 4, then 4 has tobe subtracted from the result.

The switches do not need to have header translation tables in order todo the switching, nor do they need call processing, because the RelativePort Labels have been prepared in the Gateway units, which will befurther discussed later.

The switches may move the used labels to the end of the Stack once theyhave been used. An advantage of using Relative Port Labels is that oncethe Network has been traversed, the path traversed across the Networkcan be deduced from the used Relative Port Labels. This is not possibleif basic Port Label Switching was used.

A way that the basic Port Label Switching arrangement could be used tocreate a form or reverse addressing is as follows. Once the SignificantLabel of a message has been used by a switch, then the contents of theSignificant Label can be replaced with the numerical identity of theinput traffic port by which that message entered the switch. Providedthis was done by all the traversed switches, then the resulting Stack ofLabels should indicate the path back through the network using the PortLabel Switching arrangement.

Another characteristic of Relative Port Label Switching is the abilityto have Service Domain Permits. FIG. 10 shows several packets fromdifferent ports all being switched through to port 3. In order to ensurethat Port 3 does not have to handle too much traffic and consequentialtraffic discarding, then a protection mechanism is required. Theprotection mechanism is not to prevent traffic being discarded by oneservice because that service is sending too much traffic via Port 3, butto make sure that one service sending too much traffic (for exampleService Domain A) does not disturb the quality of service within anotherService Domain (for example Service Domain B).

Each output port has to have a Capacity Allocation set for each ServiceDomain permitted to use that output port. The sum of those CapacityAllocations should not exceed the capacity of that output port, see FIG.11. When a Service Domain does exceed its permitted Capacity Allocationthen discards may occur and a Service Domain Permit Violation may beinitiated. The Capacity Allocations may include Bandwidth Parameters,Queuing Parameters, Buffering Parameters etc.

It should be noted that Service Domain Permits, although they aresimilar to the Output Attributes and/or Input Cognisant Attributesassociated with Single Link Interfaces described in Patent ApplicationNo. GB0130730.5, are additional functions that are required for RelativePort Label Switching.

Relative Port Label Switching can be used for carrying IP traffic acrossa network, provided the number of labels in a stack equals the number ofswitches to be traversed. In order to do this an entry Gateway wouldhave to determine from the IP address the route to be taken across theNetwork and generate the appropriate valid Stack of Relative PortLabels. This would not be so easy for a random meandering Network, butwould be relatively straightforward for a structured Network of the formshown in FIG. 1.

All the switches at the Edge Nodes, AREA Nodes and STAR Nodes areRelative Port Label switches.

The Gateways have to format the traffic to be carried into thecell/packet/frames with the Stack of Relative Port Labels. (Similar tothe ATM Adaptation Layer.) To carry Dial-Up type traffic across aRegular Network, call processing must be able to create the completeStack of Relative Port Labels. Call processing intelligence is only atthe Edge Nodes.

To go between the Gateways attached to the same Edge Node, as shown inFIG. 2, requires a Stack of Labels, with only one Valid Relative PortLabel as there is only one switch to traverse. Each cell, packet orframe of a call leaving a Gateway carries a Stack with one ValidRelative Port Label. This arrangement does not need the Packet TrafficOptimisation (PTO) Algorithm as described in Patent Application No.GB0130729.7.

If there is call processing intelligence at the Edge Node attached tothe two Gateways, then the one Valid Relative Port Label can beproduced.

To go between the Gateways attached to Different Edge Nodes, which areconnected to the same AREA Node, as shown in FIG. 3, requires a Stack ofLabels with three Valid Relative Port Labels as there are three switchesto traverse. Each cell, packet or frame of a call leaving a Gatewaycarries a Stack of three Valid Relative Port Labels. This arrangementuses the Packet Traffic Optimisation Algorithm as described in PatentApplication No. GB0130729.7.

If there is call processing intelligence at both the Edge Nodes attachedto the two Gateways, then the three Valid Labels can be produced:provided there is signalling communication between the Intelligent callprocessing functions at the two Edge Nodes: and consequently a SimpleTransit Core (STC) function, as described by the PTO method in PatentApplication No. GB0130729.7, can operate in the AREA Node. The AREA Nodeis a traversed switch, which is not associated with an intelligent node,yet it provides per call consolidation using the PTO protected managedover-provisioning algorithm.

To go between the Gateways attached to Different Edge Nodes, which arenot in the same AREA, as shown in FIG. 4, requires a Stack of Labelswith five Valid Relative Port Labels, as there are five switches totraverse. Each cell, packet or frame of a call leaving a Gateway carriesa Stack of five Valid Relative Port Labels. This arrangement can stilluse the PTO Algorithm as described in Patent Application No.GB0130729.7.

If there is call processing intelligence at both the Edge Nodes attachedto the two Gateways, then the five Valid Labels can be produced:provided there is signalling communication between the Intelligent callprocessing functions at the two Edge Nodes; and provided that the AREANodes (X and Z) act only as consolidating crossconnects: andconsequently a Simple Transit Core (STC) function, as described by thePTO method in Patent Application No. GB0130729.7, can operate in theSTAR Node (Y). STAR Node (Y) is a traversed switch, which is notassociated with an intelligent node, yet it provides per callconsolidation using the PTO protected managed over-provisioningalgorithm. The AREA Nodes (X and Z) are traversed switches, which arenot associated with intelligent nodes, but they only provide fixedconsolidation under static management control for paths traversing 5switches.

There are some benefits that result from using regular networktopologies of the form shown in FIGS. 5 and 8. One is that certainnumbers of nodes have to be traversed, e.g. 1, 3 of 5. If Point Mesheswere not included then in FIG. 8 it would be 1, 2 or 3 Nodes.Consequently the number of Valid Labels in a header should correspond tothe number of nodes to be traversed (otherwise an error can be assumed).There are also some other conditions which have to apply. In FIG. 5 ifthe Header only has one label then that label should not indicate anoutput port that is connected to an AREA; to be valid it should point toa port connected to a Gateway. It also follows that the first label of aheader with 3 or 5 labels should not point to a port connected to aGateway.

Some rules for FIG. 5 are:

Only the last valid label should point to a port connected to a gateway.

The penultimate valid label should point to a port connected to anAllocated Edge Node.

The first valid label, of 3 or 5 valid labels, should point to a portconnected to an AREA Node.

The second valid label, of 5 valid labels should point to a portconnected to a STAR Node.

A valid label cannot be zero (otherwise it would point back to itself).

This should ensure that a path of STAR to AREA to STAR is invalid andalso AREA to EDGE to AREA is also invalid.

A practical means of applying these rules for Partially InterconnectedSTAR Networks is to allocate the links status levels: Level 1 Gateway toAllocated Edge Node Level 2 Allocated Edge Node to AREA Node Level 3AREA Node to STAR Node

Compliance to the following is required for STAR Networks: ConnectionOne Valid Rules Label Three Valid Labels Five Valid Labels First LabelLevel 1 to Level 1 to Level 2 Level 1 to Level 2 Level 1 SecondLabel —Level 2 to Level 2 Level 2 to Level 3 Third Label — Level 2 to Level 1Level 3 to Level 3 Fourth Label — — Level 3 to Level 2 Fifth Label — —Level 2 to Level 1

It is different for Partially Interconnected FLAT Networks as shown inFIG. 8 as only 2 Levels exist: Level 1 Gateway to MP/STC Node Level 2MP/STC Node to Point Mesh Node

Accordingly compliance to the following is required for FLAT NetworksWITH POINT MESHES: Connection One Rules Valid Label Three Valid LabelsFive Valid Labels First Label Level 1 to Level 1 to Level 2 Level 1 toLevel 2 Level 1 SecondLabel — Level 2 to Level 2 Level 2 to Level 2Third Label — Level 2 to Level 1 Level 2 to Level 2 Fourth Label — —Level 2 to Level 2 Fifth Label — — Level 2 to Level 1

For Partially Interconnected FLAT Networks as shown in FIG. 6 again only2 Levels exist: Level 1 Gateway to MP/STC Node Level 2 MP/STC Node toMP/STC Node

Accordingly compliance to the following is required for FLAT NetworksWITHOUT POINT MESHES: Connection One Rules Valid Label Two Valid LabelsThree Valid Labels First Label Level 1 to Level 1 to Level 2 Level 1 toLevel 2 Level 1 SecondLabel — Level 2 to Level 1 Level 2 to Level 2Third Label — — Level 2 to Level 1

In order to indicate an invalid label a Parity bit could be includedwith each label. A label of zero with bad parity can be used to indicatean invalid label (e.g. for when the label is not needed). Using parityalso helps in finding any corruption of a label. The Service DomainPermit Number can also have a parity bit.

As already mentioned, an advantage of using Relative Port Labels is thatonce the Network has been traversed the path traversed across theNetwork can be deduced from the used Relative Port Labels. This featurecan be exploited in several ways although these exploitations do tend torely on the regular nature of Partially Interconnected Star Networks andPartially Interconnected FLAT Networks.

By setting a broadcast indicator in the header of a message a BroadcastInvestigation Message can be sent with the labels initially all beingset to the invalid state: the payload may contain test andidentification information (e.g. IP address of the Originating Gateway).The Service Domain Permit Number should correspond to the Service Domainthat is being investigated, or the Service Domain Permit Number can beset to Zero (with good parity) to indicate that the investigation is notlimited to a Service Domain. At the first switch, a message is sent outfrom all ports, except the port the message arrived on, but with onelabel now set to indicate the module addition necessary to derive theoutput port number from the input port number, to create the same effectas if the label had been used and placed at the end of the stack. Thisproceeds as the network is traversed, but in order to stop messagestrying to follow inappropriate paths or going around loops etc. thencertain rules corresponding to ones listed above are also applied sothat for example a path of STAR to AREA to STAR is invalid and also AREAto EDGE to AREA is also invalid.

The use of a Broadcast message from Gateway X should result in all theother Gateways receiving a number of messages. The number of messagescorresponding to the total number of apparently acceptable CHOICEs ofrouting across the network. via 1 node via 3 nodes via 5 nodes X to A 10 10 X to B 0 2 10 X to C 0 0 8

By setting a Response indicator in the payload of a message a BroadcastInvestigation Response Message can be formed by the gateways that havereceived Broadcast Investigation Messages: again the payload containstest and identification information (e.g. IP address of respondingGateway). Hence it is possible for a Gateway to learn the labelsrequired to reach other gateways and to learn the identities of thoseGateways. This information can be used to see if there has been a changein the possible routes, because of failures or reconfigurations. Thecomplexity of forming these messages and interpreting the results is theresponsibility of the Gateways, the only special function for theRelative Port Label Switches is to handle broadcast messages and applythe Connection Rules defined above.

By using Relative Port Label Switches it is possible to do this processacross a network which uses very simple switches. There is norequirement for Header Translation Tables or Routing tables to behandled by the Relative Port Label Switches themselves.

A Service Domain Permit Violation can occur when a message has had to bediscarded. It could also be triggered at a lower level if required (say85% occupancy). The action taken by a Relative Port Label Switch when aService Domain Permit Violation is triggered is to send out a broadcastmessage (containing a Violation Indicator) for that Service Domain inthe opposite direction, i.e. back towards all the Gateways who may besupplying too much traffic, or who could supply traffic to thisparticular point of the network for that Service Domain. The Gatewayswho received the Service Domain Permit Violation messages should thenavoid using the label stacks, for the affected Service Domain, thatdirectly correspond to the one received in the Service Domain PermitViolation messages.

The object of Service Domain Permits and discarding messages is toprotect other Service Domains. They do not automatically protectcircuits within a Service Domain from affecting one another. PacketTraffic Optimisation (PTO) is a method of ensuring Dial-Up type circuitswithin a Service Domain do not interfere with one another. Whentraversing 5 Nodes, as shown in FIG. 4, and using PTO, then the Callprocessing and PTO processing should be done at the Edge Node and thenthe Gateways supplied with the required Relative Port Label Stacks bythe Edge Nodes.

Multi Protocol Label Switching (MPLS) is a recognised technique. Itneither uses the labels for the direct addressing of the output ports,nor the relative addressing of the output ports.

When a Gateway receives a Broadcast Investigation Message or a ServiceDomain Permit Violation Message, it needs to deduce the Relative PortLabels (Reverse Stack) to retrace the path back to the source of themessage. So for each label assuming it has L bits (not including parity)then:

Value of Reverse Label equals 2^(L)—Value of Original Label

This deduction has to be done for each Label.

FIGS. 12 to 18 show in considerable detail the actions that are requiredwhen traversing the 5 nodes as shown in FIG. 4.

FIG. 12 shows the initial Relative Port Label Stack. It assumes that allthe switches require L bits for each Label as they may have up to 2^(L)ports.

FIG. 13 shows the action required at the Originating Allocated EdgeNode. The Top Label is used to define the output port and is then placedat the bottom of the Stack, with the other labels shufling up oneposition. The Capacity Allocation of the Service Domain Permit should bechecked to ensure it is not exceeded.

FIG. 14 shows the action required at the Originating AREA Node Switch,and as for FIG. 13 the Top Label is used to define the output port andis then placed at the bottom of the Stack, with the other labelsshuffling up one position. The Capacity Allocation of the Service DomainPermit should be checked to ensure it is not exceeded.

FIG. 15 shows the action required at the STAR Node Switch.

FIG. 16 shows the action required at the Terminating AREA Node Switch.

FIG. 17 shows the action required at the Terminating AREA Node SwitchFIG. 18 shows the state of the labels that arrive at the terminatingGateway and how the Reverse Stack can be deduced.

It should be noted that the Capacity Allocation Parameters for eachService Domain Permit may be supplied to the Relative Port LabelSwitches via a management or a control interface. Some other informationthat may need to be supplied via a management control interface is: theLevel assigned to each link; the type of Network e.g. STAR, FLAT (withPoint Meshes), FLAT (without Point Meshes); the type of node and theformat of the header.

In order to supply management information via the normal trafficinterfaces it may be required to attach a Management Gateway to a porton a node in the network that does not normally have a directlyconnected gateway, e.g. a STAR Node. Management information received bya normal traffic interface would be switched (as indicated by theSignificant Label) through to the port to which the Management Gatewayis attached.

The present application has mentioned that once a label has been used itmay be placed at the end of the stack. This helps to indicate, to thenext switch which is the Significant Label. There are other ways ofindicating which is the Significant Label, which involve making it clearwhich labels have been used and therefore the next one in the stack isthe Significant one. This could be achieved by using individualindicators for each label, or by inverting the parity bit, or byincrementing a count value to say how many labels have been used. It isalso possible in the case of a STAR Network to deduce, from theconnection rules, which is the Significant Label although this is notthe case for a FLAT network. The Significant Label can be deduced ifsome additional information is included with the Label Stacks used in aFLAT network, such as:

-   -   the numerical identity of one relevant node (not for 5 label        stacks)    -   the numerical identity of more than one relevant nodes    -   the numerical identity of one relevant node, provided nodes are        aware of the numerical identities of nodes to which they are        connected.

The advantage of not having to change the header can simplify the switchcircuitry and may be of considerable benefit to some forms of switching,such as optical switching. Another benefit is that if a switch does notchange the contents of a message (neither header nor payload) thenfinding faults and performance monitoring may be easier.

1-15. (canceled)
 16. A communications switch, comprising: a plurality ofnumerically identified input traffic ports at which messages enter theswitch; a plurality of numerically identified output traffic ports atwhich messages leave the switch; at least one numerical processor; eachmessage entering the switch by a numerically identified input trafficport containing a header which contains a label stack that includes atleast one valid label which is a significant label; at least onesignificant label extraction means for extracting a numerical value ofthe significant label contained within the header of a particular one ofthe messages which entered the switch via a particular one of thenumerically identified input traffic ports, and for supplying theextracted numerical value of the significant label to the at least onenumerical processor operative for using the significant label of theparticular one of the messages and a numerical value of the particularone of the numerically identified input traffic ports to form anumerical result which directly equates to a number of the numericallyidentified output traffic port by which said particular one of themessages leaves the switch.
 17. The communications switch as claimed inclaim 16, wherein a numerically identified input traffic port and anumerically identified output traffic port form a duplex pair having thesame numerical identity.
 18. The communications switch as claimed inclaim 16, wherein the header contains multiple valid labels in the labelstack, and wherein a first label in the stack received by the switch isthe significant label.
 19. The communications switch as claimed in claim18, wherein once the numerical value of the significant label has beenextracted, the significant label is moved to a last position in thestack.
 20. The communications switch as claimed in claim 16, wherein thenumerical result is equal to the numerical value of the significantlabel.
 21. The communications switch as claimed in claim 16, wherein thenumerical result is equal to a modulo addition of the numerical value ofthe significant label and the numerical value of the particular one ofthe numerically identified input traffic ports.
 22. The communicationsswitch as claimed in claim 21, and an interface for applying a set ofconnection rules, and wherein the messages are not forwarded from theswitch unless the messages comply with the applied set of connectionrules.
 23. The communications switch as claimed in claim 22, wherein theheader of the particular one of the messages includes a broadcastindicator, and wherein the particular one of the messages leaves theswitch via all the numerically identified output traffic ports, exceptthe numerically identified output traffic port which has the same numberas the numerically identified input traffic port by which the particularone of the messages entered the switch.
 24. The communications switch asclaimed in claim 23, wherein each message leaving the switch has a usedsignificant label set to the same numerical value as a similar messagewould have if the similar message had entered on the same numericallyidentified input traffic port and left on the same numericallyidentified output traffic port, except that the similar message does notinclude the broadcast indicator.
 25. The communications switch asclaimed in claim 16, and separate and additional gateways for generatingthe messages with label stacks, for receiving the messages, forgenerating broadcast messages, for receiving the broadcast messages, forgenerating broadcast response messages using a reverse label stack, andfor receiving the broadcast messages containing a violation indicator.26. The communications switch as claimed in claim 16, wherein the headerof each message also includes a service domain permit number to indicateto which service domain a message belongs; and means for comparing aquantity of traffic from each service domain that is forwarded to anumerically identified output traffic port against capacity allocationparameters held for a respective service domain for the numericallyidentified output traffic port.
 27. The communications switch as claimedin claim 26, wherein if a numerically identified output traffic port isaffected by the capacity allocation parameters being exceeded, then abroadcast message containing a violation indicator is initiated in anopposite direction by the affected numerically identified output trafficport via the numerically identified input traffic port having the samenumerical identity.
 28. A partially interconnected network, comprising:a plurality of communications switches connected to form the network,each switch as claimed in claim 16, the plurality of switches beingallocated nodes or star nodes, each allocated node being allocated toone of a number of areas, a plurality of point-to-point interconnectionsbetween the allocated nodes and the star nodes, wherein a number ofareas with allocated nodes interconnected to an individual star nodeforms a number of routes from an individual star node, the allocatednodes of a first of the areas being interconnected to a set comprisingsome, but not all, of the star nodes, and wherein further of the areasare similarly interconnected to further sets each comprising star nodes,and where there is at least one interconnection choice between any twoallocated nodes in different areas.
 29. The network as claimed in claim28, wherein the plurality of switches represent at least six topologicalnodes; wherein a topological node is a single physical node, or a groupof interconnected physical nodes, or part of a physical node, or part ofa group of interconnected physical nodes, or parts of physical nodes;each topological node having at least three point-to-point topologicallinks connecting it to some, but not all, of the plurality oftopological nodes; and where there is at least one choice of routingbetween any two topological nodes, and where the at least one choice ofrouting comprises either two point-to-point topological links connectedin series at another of the topological nodes, or a directpoint-to-point topological link between the two topological nodes. 30.The network as claimed in claim 28, wherein the plurality of switchesrepresent a plurality of nodes, wherein at least one of the plurality ofnodes includes a switching means for carrying out a simple transit corefunction, and wherein three or more of the plurality of nodes include asingle link interface having associated output attributes and/or inputcognizant attributes, wherein each simple transit core function at onenode is not logically connected to another simple transit core functionat another node, wherein each simple transit core function at one nodeis logically connected to at least three single link interfaces at othernodes, and wherein the nodes including single link interfaces which areconnected to one instance of a node arranged to carry out a simpletransit core function are controlled by respective intercommunicatingconnection acceptance control processes according to the respectiveoutput attributes and/or input cognizant attributes.